1. Field of the Invention
The present invention is related to a membrane zeta potential measuring system, and more particularly to a measuring system which is able to measure both the membrane pore zeta potential and the membrane surface zeta potential.
2. Description of the Prior Art
Membrane separation is now a widely utilized technique in biotechnology, pharmaceutical and electronic industries for ultrafiltration operations. Fouling, a deposition on the membrane surface or in membrane pores, is the major problem in membrane separation processes resulting in a considerable reduction of the transmembrane permeability, a loss of valuable products and consequently an increase in operational costs.
Most membranes acquire an electric surface charge when brought into contact with an aqueous solution. The surface charge has been utilized as an important correlating parameter to study the fouling characteristics of ultrafiltration membranes with the greatest fouling typically seen under conditions where the solute and the membrane have opposite net charges. Zeta potential is an important and reliable indicator of this membrane surface charge, and knowledge of zeta potential is essential for the design and operation of membrane processes.
Currently, the most widely used tool for determining the zeta potential of membranes is the streaming potential. The streaming potential is generated when a fluid flows through a channel with a charged surface. In the charged channel, an electric double layer is formed at the phase boundary between the solid and liquid.
Streaming potential measurements can be performed in two different ways: by flow through membrane pores (transmembrane streaming potential) or by flow across the top surface of the membrane (tangential streaming flow).
In order to evaluate zeta potential from the streaming potential data, some important factors such as the overlap of electric double layers in the pore, the pore size distribution, and the detailed morphology and connectivity of the pore structure . . . etc., would need to be accounted for. Since these phenomena are largely unavailable, the data are mostly analyzed to obtain the “apparent zeta potential” by utilizing the Helmholtz-Smoluchowski equation or modified ones thereof.
Currently, commercial membranes for either research or industrial usages are often directly utilized based on the property information provided by the manufacturers; however, these provided membrane properties, especially the membrane charge herein, depend significantly on the physico-chemical properties of the solutions or suspensions contacted with the membrane.
Therefore, having a reliable measuring system to determine the membrane zeta potential under different conditions will provide useful information for the design and operation of a membrane system, and through which the operational costs will be greatly reduced.